We really like [name_m]Simon[/name_m] for a boy, what would you name his sister?
The options are:
[name_f]Lucy[/name_f]
[name_f]Clara[/name_f]
[name_f]Tabitha[/name_f]
[name_f]Esme[/name_f]
[name_u]Adair[/name_u]
[name_f]Rosie[/name_f]
[name_f]Beatrix[/name_f]
[name_f]Alexandra[/name_f]
[name_f]Millie[/name_f]
[name_f]Fenella[/name_f]
[name_f]Tabitha[/name_f]…[name_m]Simon[/name_m] and [name_f]Tabitha[/name_f].
My favourites are:
[name_m]Simon[/name_m] & [name_f]Clara[/name_f]
[name_m]Simon[/name_m] & [name_f]Tabitha[/name_f]
[name_m]Simon[/name_m] & [name_f]Beatrix[/name_f]
I think that they all go with [name_m]Simon[/name_m]’s quiet vintage vibe well. If I had to choose just one, I’d go with [name_f]Clara[/name_f]. She’s short and sweet and doesn’t need a nickname.
From your list, I like [name_f]Clara[/name_f] and [name_f]Tabitha[/name_f].
I especially like that [name_f]Clara[/name_f] has a meaning of “clear”, while [name_m]Simon[/name_m] means “listener”, so it gives them a bit of further connection, meaning-wise.
[name_m]Simon[/name_m] feels like a smart, distinguished, understated choice with lots of history.
[name_f]Clara[/name_f], [name_f]Esme[/name_f] and [name_f]Lucy[/name_f] match especially perfectly to me, but I’d also like to throw my hat in the ring for [name_f]Fenella[/name_f]. A lovely, distinctive choice that I hardly ever see considered, even on Nameberry!
[name_f]Esme[/name_f], [name_f]Rosie[/name_f] or [name_f]Fenella[/name_f]
[name_f]Finella[/name_f] [name_f]Esme[/name_f] - Fefe!
All of them would match pretty well except [name_u]Adair[/name_u], [name_f]Fenella[/name_f], and [name_f]Alexandra[/name_f]. [name_f]Millie[/name_f] and [name_f]Esme[/name_f] are my favorites!
[name_f]Millie[/name_f] [name_f]Claudia[/name_f]
[name_f]Millie[/name_f] [name_f]Rose[/name_f]
[name_f]Millie[/name_f] [name_f]Iris[/name_f]
[name_f]Millie[/name_f] [name_f]Tabitha[/name_f]
[name_f]Millie[/name_f] [name_f]Ismay[/name_f]
[name_f]Millie[/name_f] [name_f]Rowena[/name_f]
[name_f]Millie[/name_f] [name_f]Aster[/name_f]
[name_f]Millie[/name_f] [name_f]Joy[/name_f]
[name_f]Millie[/name_f] [name_u]Quinn[/name_u]
[name_f]Millie[/name_f] [name_f]Florence[/name_f]
[name_f]Millie[/name_f] [name_u]Wren[/name_u]
[name_f]Millie[/name_f] [name_u]Phoenix[/name_u]
[name_f]Esme[/name_f] [name_f]Isla[/name_f]
[name_f]Esme[/name_f] [name_f]Florence[/name_f]
[name_f]Esme[/name_f] [name_f]Tillie[/name_f]
[name_f]Esme[/name_f] [name_u]Wynn[/name_u]
[name_f]Esme[/name_f] [name_f]Rowena[/name_f]
[name_f]Esme[/name_f] [name_u]Wren[/name_u]
[name_f]Esme[/name_f] [name_f]Fern[/name_f]
[name_f]Esme[/name_f] [name_f]Eileen[/name_f]
[name_f]Esme[/name_f] [name_f]Prudence[/name_f]
[name_f]Esme[/name_f] [name_f]Olive[/name_f]
[name_f]Lucy[/name_f], [name_f]Beatrix[/name_f], and [name_f]Millie[/name_f] are my favorites from your list!
[name_f]Lucy[/name_f] and [name_f]Clara[/name_f] are my top picks, and also like [name_f]Esme[/name_f] and [name_f]Rosie[/name_f] with [name_m]Simon[/name_m].
I like [name_f]Fenella[/name_f] and [name_f]Rosie[/name_f] with [name_m]Simon[/name_m].
[name_m]Simon[/name_m] and [name_f]Lucy[/name_f]. 
[name_f]Tabitha[/name_f], [name_f]Clara[/name_f], [name_f]Fenella[/name_f] or [name_f]Esme[/name_f]. ([name_f]Lucy[/name_f] matches too, it’s just far too popular for me!)
I like [name_f]Tabitha[/name_f], [name_f]Clara[/name_f], [name_f]Beatrix[/name_f] and [name_f]Fenella[/name_f]. I wanted to write ‘but particularly ___’ and when I tried to pick my favourite I just couldn’t! I think you have a lovely collection of names to chose from.
If it was me I think I’d steer clear of a diminutive name for your girl. With [name_m]Simon[/name_m] being such a distinguished, solid name I’d also want one for his twin. So I’d use [name_f]Rose[/name_f] and [name_f]Amelie[/name_f] (or [name_f]Camille[/name_f], or [name_f]Emmeline[/name_f], or [name_f]Matilda[/name_f], or [name_f]Emilia[/name_f]) instead of [name_f]Rosie[/name_f] and [name_f]Millie[/name_f]. Also, while I do really like [name_u]Adair[/name_u] for girl and boy actually, in this twin pairing I imagine on paper people would assume you had b/b twins - I think I would. Now if I loved the name hard enough I don’t think that would bother me much, but it’s something to consider if that would bother you.
Good luck
I like [name_m]Simon[/name_m] with [name_f]Fenella[/name_f], [name_f]Tabitha[/name_f], and [name_f]Lucy[/name_f].
Favorites:
[name_f]Lucy[/name_f] - This is such a sweet set, even if [name_f]Lucy[/name_f] is popular.
[name_f]Clara[/name_f] - Another perfect match, and I like that both names have five letters and aren’t nicknames.
[name_f]Beatrix[/name_f] - It’s not quite as perfect a match as the other two, but it’s one of my favorite names, and I like the sort of quirky British feeling it has next to [name_m]Simon[/name_m].
Ok:
[name_f]Millie[/name_f] - [name_m]Don[/name_m]'t love that it’s a nickname, feels very incomplete.
[name_f]Rosie[/name_f] - I would actually love [name_f]Rose[/name_f] nn [name_f]Rosie[/name_f] with [name_m]Simon[/name_m], but [name_f]Rosie[/name_f] on its own doesn’t match.
[name_f]Tabitha[/name_f] - I love the [name_f]Beatrix[/name_f] [name_m]Potter[/name_m] vibe that these names give me together, but [name_f]Tabitha[/name_f] still seems a little dusty and puritan-y next to more modern [name_m]Simon[/name_m].
[name_f]Esme[/name_f] - Nothing really wrong here, but it seems sort of too romantic and [name_m]French[/name_m] next to simple [name_m]Simon[/name_m].
[name_m]Don[/name_m]'t [name_u]Love[/name_u]:
[name_u]Adair[/name_u] - Too unisex next to [name_m]Simon[/name_m].
[name_f]Alexandra[/name_f] - A little outdated and an odd combo with [name_m]Simon[/name_m].
[name_f]Fenella[/name_f] - I’m sorry, I really just think of [name_u]Fennel[/name_u].
First choice [name_f]Clara[/name_f]
Second choice [name_f]Esme[/name_f]
I love the options of [name_f]Millie[/name_f] and [name_f]Esme[/name_f]!
I love [name_f]Lucy[/name_f] and [name_f]Beatrix[/name_f] with [name_m]Simon[/name_m]!
[name_m]Simon[/name_m] and [name_f]Clara[/name_f] (my favourite)
[name_m]Simon[/name_m] and [name_f]Lucy[/name_f]
[name_m]Simon[/name_m] and [name_f]Rose[/name_f] (nn [name_f]Rosie[/name_f])